Gmail rejecting emails from the site

[Jeremiah Roth]

Email from our site (password reset, contact hosts) are being rejected by gmail recipients. This is because gmail requires additional things for IPv6.

relay=gmail-smtp-in.l.google.com[2607:f8b0:400d:c02::1b]:25, delay=0.48, delays=0.04/0/0.15/0.29, dsn=5.7.1, status=bounced (host gmail-smtp-in.l.google.com[2607:f8b0:400d:c02::1b] said: 550-5.7.1 [2600:3c03::f03c:91ff:fe59:7a05] Our system has detected that this 550-5.7.1 message does not meet IPv6 sending guidelines regarding PTR records 550-5.7.1 and authentication. Please review 550-5.7.1 https://support.google.com/mail/?p=IPv6AuthError for more information 550 5.7.1 . p125si7163239qkb.317 - gsmtp (in reply to end of DATA command))

[Jeremiah Roth]

Since we're already using Mailgun, I set up Postfix to use Mailgun as a relay, which should take care of all gmail's requirements. I tested by creating a new user account with [e-mail], and received the email (though in my spam box).

I kept getting 'SASL authentication failure: No worthy mechs found' errors until I installed cyrus-sasl-plain. cyrus-sasl and cyrus-sasl-lib was already installed but wasn't enough.

Some issues to keep under consideration:

• The email comes from '[e-mail] via drinkingliberally.org', which might contribute to the spam rating. Need to investigate this.
• In mailgun logs, the envelope sender is '[e-mail]' which should be fine since the MIME sender is correct ([e-mail])
• Because of the number of spam users created on the site and the need to send an account setup email for each, this will increase our Mailgun usage. Which means we need to prioritize blocking these spam accounts.

[Jeremiah Roth]

Reference

• https://documentation.mailgun.com/user_manual.html#smtp-relay
• https://community.rackspace.com/products/f/28/t/3897
• http://serverfault.com/questions/211749/sending-mail-from-postfix-via-gmail-unable-to-get-local-issuer-certificate-cer